The invention relates to fibers made of partly crystal-line copolymers of polycyclic olefins.
Polyolefin fibers based on polyethylene and polypropylene are already known. A very advantageous property of these polyolefin fibers is their high solvent resistance. They are essentially stable to all polar solvents (for example ketones, alcohols, organic acids, ester compounds, amide compounds) and aqueous media (for example aqueous acids, alkalis), and at room temperature are also resistant to nonpolar solvents such as saturated hydrocarbons (for example oils, petroleum fractions). This property, combined with a high chemical resistance, has given the polyolefin fibers wide areas of application in the textile sector and in industry. Highly oriented fibers made of high-molecular-weight PE are known for their very high tensile strength at room temperature. PE and PP fibers are also used for the manufacture of woven fabrics and nonwovens.
The thermal shape stability, for example in connection with the sterilizability or other processes in which higher temperatures occur (for example, nonwovens for filtering of hot water and gas), frequently plays an important role here. Unfavorably, the mechanical properties of PE fibers begin to fall off only just above room temperature. A significant deterioration is observed above about 70 to 80xc2x0 C.
Cycloolefin copolymers incorporating a high proportion of cycloolefin and also cycloolefin homopolymers have, because of their high glass transition temperature, very high thermal shape stability and hence good mechanical properties. Furthermore, they have outstanding resistance to polar solvents such as water, alcohol, acetone and dimethylformamide, and also to aqueous acids and alkalis. However, on the unfavorable side, they dissolve readily in aliphatic and aromatic hydrocarbons or they are greatly swollen by these.
It is an object of the invention to provide polyolefin fibers which are comparable with polyethylene and polypropylene fibers in respect of their solvent resistance and at the same time have a higher thermal shape stability than these known polyolefin fibers and can be spun from the melt.
It has been found that this object can be achieved by fibers made of partly crystalline cycloolefin copolymers which contain less than 100 ppm (based on the total weight of the polymer) of catalyst residues.
The preparation of partly crystalline cycloolefin copolymers is described in EP-A-0 503 422. Tests have shown that the polymers thus prepared contain above 100 ppm of catalyst residues (i.e. metallocene and cocatalyst residues). During processing via the melt (at about 300xc2x0 C.) these products prove to be thermally labile. This is shown by the polymer turning brown. Thin pressed plates (thickness 200 xcexcm) showed distinct gel particles (fish eyes) which probably arose through localized crosslinking of the polymer, triggered by catalyst residues. Spinning tests on fibers produced in accordance with EP-A 503 422 gave unsatisfactory results, since the gel particles led to fiber breakage. It was established that such cycloolefin polymers are only suitable for fiber production if the residual catalyst content is less than 100 ppm.
Cycloolefins polymerize in bulk or in solvents in the presence of metallocene catalysts with retention of the rings (EP 407870, DE 84036264). The solvents used are mainly hydrocarbons.
The invention accordingly provides fibers which comprise at least one cycloolefin copolymer which can be prepared by polymerization of from 30 to 99.9% by weight, based on the total amount of monomers, of at least one symmetrical, polycyclic olefin of the formula I, II, III, IV, V or VI 
in which R1, R2, R3, R4, R5, R6, R7 and R8 are identical or different and are a hydrogen atom, a C6-C16-aryl or a C1-C8-alkyl radical,
from 0 to 50% by weight, based on the total amount of monomers, of a monocyclic olefin of the formula VII 
in which n is a number from 2 to 10, and from 70 to 0.1% by weight, based on the total amount of monomers, of at least one acyclic olefin of the formula VIII 
in which R9, R10, R11 and R12 are identical or different and are a hydrogen atom or a C1-C8-alkyl radical or a C6-C16-aryl radical, at temperatures from xe2x88x9278 to 150xc2x0 C. and a pressure from 0.01 to 64 bar, in the presence of a catalyst which comprises an aluminoxane of the formula IX 
for the linear type and/or of the formula X 
for the cyclic type, where in the formulae IX and X the radicals R13 are identical or different and are a C1-C6-alkyl group or phenyl or benzyl and n is an integer from 0 to 50, and a metallocene of the formula XI 
in which
M1 is titanium, zirconium, hafnium, vanadium, niobium or tantalum,
R14 and R15 are identical or different and are a hydrogen atom, a halogen atom, a C1-C10-alkyl group, a C1-C10-alkoxy group, a C6-C10-aryl group, a C6-C10-aryloxy group, a C2-C10-alkenyl group, a C7-C40-arylalkyl group, a C7-C40-alkylaryl group or a C8-C40-arylalkenyl group,
m=1 or 2
R16 and R17 are different and are a monocyclic or polycyclic hydrocarbon radical which can form a sandwich structure with the central atom M1, where the part of the molecule formed by R16, R17 and M1 has C1 symmetry,
R18 is 
xe2x80x83xe2x95x90BR19xe2x95x90AlR19, xe2x80x94Gexe2x80x94, xe2x80x94Snxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x95x90SO, xe2x95x90SO2, xe2x95x90NR19, xe2x95x90CO, xe2x95x90PR19 or xe2x95x90P(O)R19, where R19, R20 and R21 are identical or different and are a hydrogen atom, a halogen atom, a C1-C10-alkyl group, a C1-C10-fluoroalkyl group, a C6-C10-fluoroaryl group, a C6-C10-aryl group, a C1-C10-alkoxy group, a C2-C10-alkenyl group, a C7-C40-arylalkyl group, a C8-C40-arylalkenyl group or a C7-C40-alkylaryl group or R19 and R20 or R19 and R21 form a ring with the atoms linking them in each case, and
M2 is silicon, germanium or tin, wherein the residual catalyst content is less than 100 ppm.
Alkyl is here a straight-chain or branched alkyl.
The monocyclic olefin of the formula VII may, for the purposes of the invention, also be substituted (for example by aryl or alkyl radicals).
The polymerization is preferably carried out in the liquid cycloolefin monomer, cycloolefin monomer mixture or in concentrated solutions.
In the polymerization reaction, at least one symmetrical polycyclic olefin of the formula I, II, III, IV, V or VI, preferably a symmetrical polycyclic olefin of the formula I or III in which R1, R2, R3, R4, R5, R6, R7 and R8 are identical or different and are a hydrogen atom or a C1-C8-alkyl radical, is polymerized.
If desired, a monocyclic olefin of the formula VII in which n is a number from 2 to 10 is also used. Another comonomer is an acyclic olefin of the formula VIII in which R9, R10, R11 and R12 are identical or different and are a hydrogen atom or a C1-C8-alkyl radical. Ethylene or propylene is preferred.
In particular, copolymers of polycyclic olefins, preferably of the formulae I and III, with the acyclic olefins of the formula VIII are prepared.
Particularly preferred cycloolefins are norbornene and tetracyclododecene, with these able to be substituted by (C1-C6)-alkyl. They are preferably copolymerized with ethylene; ethylene/norbornene copolymers are of particular importance.
The cycloolefin copolymers of the invention are preferably obtained when the ratio of cycloolefin to acyclic olefin is optimized.
If the selected concentration of the acyclic olefin at a given cycloolefin concentration is too high, the cycloolefin content of the copolymer falls below 50 mol %. The melting point is shifted to lower temperatures or disappears entirely.
If the concentration of the acyclic olefin at a given cycloolefin concentration is too low, there is a fall, in particular, in the activity of catalysis and in the molecular weight of the copolymer.
The cycloolefin copolymers prepared according to the process described here contain the symmetrical polycyclic 30 olefin of the formula I, II, III, IV, V or VI in an amount from 41 to 59 mol %, preferably from 45 to 55 mol %, particularly preferably from 48 to 52 mol %, in each case based on the total amount of monomers. The acyclic olefin of the formula VIII is contained in the cycloolefin copolymers in an amount from 59 to 41 mol %, preferably from 55 to 45 mol %, particularly preferably from 52 to 48 mol %, in each case based on the total amount of monomers.
Most preferred are cycloolefin copolymers containing the symmetrical polycyclic olefin of the formula I, II, III, IV, V or VI and the acyclic olefin of the formula VIII in a molar ratio of 1:1.
The monocyclic olefin of the formula VII is contained in the cycloolefin copolymers in an amount of less than 5 mol %.
Polycyclic olefins, monocyclic olefins and acyclic olefins are to be taken to include mixtures of two or more olefins of the respective type. This means that tercopolymers and multicopolymers too, can be prepared, as well as polycyclic bicopolymers, according to the polymerization process described. Copolymers of the cycloolefins of the formula VII with the acyclic olefins of the formula VIII can also be advantageously prepared according to the process described. Among the cycloolefins of the formula VII, preference is given to cyclopentene, which may be substituted.
The glass transition temperature of the cycloolefin copolymers of the invention is preferably 100-250xc2x0 C., particularly preferably from 110 to 220xc2x0 C. and most preferably from 120 to 150xc2x0 C.
The melting point preferably lies in the range from 200 to 600xc2x0 C., particularly preferably from 230 to 400xc2x0 C. and most preferably from 260 to 300xc2x0 C.
The catalyst to be used for the polymerization process described comprises an aluminoxane and at least one metallocene (transition metal component) of the formula 
In the formula XI, M1 is a metal selected from the group comprising titanium, zirconium, hafnium, vanadium, niobium and tantalum, preferably zirconium and hafnium, particular preference being given to using zirconium.
R14 and R15 are identical or different and are a hydrogen atom, a C1-C10-, preferably C1-C3-, alkyl group, a C1-C10-, preferably C1-C3-, alkoxy group, a C6-C10-, preferably C6-C8-, aryl group, a C6-C10-, preferably C6-C8-, aryloxy group, a C2-C10-, preferably C2-C4-, alkenyl group, a C7-C40-, preferably C7-C10-, arylalkyl group, a C7-C40-, preferably C7-C12-, alkylaryl group, a C8-C40-, preferably C8-C12-, arylalkenyl group or a halogen atom, preferably chlorine. m is 1 or 2.
Preferably R16 is fluorenyl, indenyl, cyclopentadienyl and R17 is cyclopentadienyl and indenyl, where these radicals may be substituted.
The part of the metallocene formed by the central atom M1 and the substituents R16-R17 has C1 symmetry.
R18 is a single-membered or multi-membered bridge which links the radicals R16 and R17 and is preferably 
xe2x95x90BR19xe2x95x90AlR19, xe2x80x94Gexe2x80x94, xe2x80x94Snxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x95x90SO, xe2x95x90SO2,
xe2x95x90NR19, xe2x95x90CO, xe2x95x90PR19 or xe2x95x90P(O)R19,
where R19, R20 and R21 are identical or different and are a hydrogen atom, a halogen atom, a C1-C10-alkyl group, a C1-C10-fluoroalkyl group, a C6-C10-aryl group, a C1-C10-alkoxy group, a C2-C10-alkenyl group, a C7-C40-arylalkyl group, a C8-C40-arylalkenyl group or a C7-C40-alkylaryl group, or R19 and R20 or R19 and R21 form a ring together with the atoms linking them in each case.
Preferably R18 is a radical 
and particularly preferably 
Of the radicals R19xe2x80x94M2xe2x80x94R20, dimethylsilyl is of particular importance.
M2 is silicon, germanium or tin, preferably silicon or germanium, particularly preferably silicon.
The bridged metallocenes can be prepared according to the following known reaction scheme: 
The above reaction scheme is also valid for the cases R19xe2x95x90R20 and/or R14xe2x95x90R15 (Journal of Organometallic Chem. 288 (1985) 63-67 and EP-A 320 762).
Of the metallocenes of the invention of the formula XI, which all have C1 symmetry in the part of the molecule formed by the central atom M1 and the substituents R16-R17 (i.e. this part of the molecule has no higher symmetry elements and can be brought into coincident superposition with itself only by rotation through 360xc2x0, a single-fold axis), particular preference is given to:
isopropylene(9-fluorenyl) (1-(3-ethyl)cyclopentadienyl)zirconium dichloride,
isopropylene(9-fluorenyl)(1-(3-isopropyl)cyclopentadienyl)zirconium dichloride,
isopropylene(9-fluorenyl)(1-(3-methyl)cyclopentadienyl)zirconium dichloride,
diphenylmethylene(9-fluorenyl)(1-(3-methyl)cyclopentadienyl)zirconium dichloride,
methylphenylmethylene(9-fluorenyl)(1-(3-methyl)cyclopentadienyl)zirconium dichloride,
dimethylsilyl(9-fluorenyl)(1-(3-isopropyl)cyclopentadienyl)zirconium dichloride,
dimethylsilyl(9-fluorenyl)(1-(3-methyl)cyclopentadienyl)zirconium dichloride,
diphenylsilyl(9-fluorenyl)(1-(3-methyl)cyclopentadienyl)zirconium dichloride,
diphenylmethylene(9-fluorenyl)(1-(3-tert-butyl)cyclopentadienyl)zirconium dichloride,
isopropenyl(2,3,4,5-tetramethylcyclopentadienyl)-(1-(3-methyl)cyclopentadienyl)zirconium dichloride and
isopropylene(9-fluorenyl)(1-(3-tert-butyl)cyclopentadienyl)zirconium dichloride and the corresponding hafnium dichlorides.
Particular preference is given to:
isopropylene(9-fluorenyl)(1-(3-methyl)cyclopentadienyl)zirconium dichloride.
For an explanation of C1 symmetry, see K. Mislow xe2x80x9cEinfxc3xchrung in die Stereochemiexe2x80x9d, Verlag Chemie, 1st edition, 1967, p. 23 ff.
General preference is given to ligand systems (R16-R18-R17) which can exert a different steric effect on the ligands R14 and R15. The nature of the ligands R14 and R15 is of no importance here.
The cocatalyst is (preferably) an aluminoxane of the formula IX and/or the formula X. In these formulae, the radicals R13 can be identical or different and are a C1-C6-alkyl group, preferably methyl, ethyl or isobutyl, butyl or neopentyl, or phenyl or benzyl. Particular preference is given to methyl. n is an integer from 0 to 50, preferably from 5 to 40.
The aluminoxane can be prepared in various ways by known processes. One of the methods is, for example, reacting an aluminum-hydrocarbon compound and/or a hydrido-aluminum-hydrocarbon compound with water (gaseous, solid, liquid or boundxe2x80x94for example as water of crystallization) in an inert solvent (such as toluene). To prepare an aluminoxane having different alkyl groups R13, two different trialkylaluminums (AlR3+AlRxe2x80x23) are reacted with water in accordance with the desired composition (cf. S. Pasynkiewicz, Polyhedron 9 (1990) 429 and EP-A 302 424).
The exact structure of the aluminoxanes is not known.
Independently of the method of preparation, a varying content of unreacted aluminum starting compound, which is present in free form or as an adduct, is common to all aluminoxane solutions.
It is possible to preactivate the metallocene with an aluminoxane of the formula IX and/or X prior to use in the polymerization reaction. The polymerization activity is thereby significantly increased.
The preactivation of the transition metal compound is carried out in solution. The metallocene is here preferably dissolved in a solution of the aluminoxane in an inert hydrocarbon. Suitable inert hydrocarbons are aliphatic or aromatic hydrocarbons. Preference is given to using toluene.
The concentration of the aluminoxane in the solution lies in the range from about 1 mol % up to the saturation limit, preferably from 5 to 30 mol %, in each case based on the total solution. The metallocene can be used in the same concentration, but is preferably used in an amount of 10xe2x88x924xe2x88x921 mol per mol of aluminoxane. The preactivation time is from 5 minutes to 60 hours, preferably from 5 to 60 minutes. The preactivation is carried out at a temperature from xe2x88x9278xc2x0 C. to 100xc2x0 C., preferably from 0 to 70xc2x0 C.
The metallocene can also be prepolymerized or applied to a support. For prepolymerization, the (or one of the) olefin(s) used in the polymerization is preferably employed.
Suitable supports are, for example, silica gels, aluminum oxides, solid aluminoxane or other inorganic support materials. Another suitable support material is a polyolefin powder in finely divided form.
A further possible embodiment of the process of the invention comprises using, in place of or in addition to an aluminoxane, a salt-like compound of the formula RxNH4xe2x88x92xBRxe2x80x24 or the formula R3PHBRxe2x80x24 as cocatalyst. Here x=1, 2 or 3, R=alkyl or aryl, identical or different, and Rxe2x80x2=aryl which can also be fluorinated or partially fluorinated. In this case the catalyst comprises the reaction product of a metallocene with one of the specified compounds (EP-A 277 004).
If solvent is added to the reaction mixture, it is a conventional inert solvent such as, for example, an aliphatic or cycloaliphatic hydrocarbon, a petroleum or hydrogenated diesel oil fraction or toluene.
The metallocene compound is used in a concentration, based on the transition metal, from 10xe2x88x923 to 10xe2x88x928, preferably from 10xe2x88x924 to 10xe2x88x927, mol of transition metal per dm3 of reactor volume. The aluminoxane is used in a concentration from 10xe2x88x924 to 10xe2x88x927, preferably from 10xe2x88x924 to 2xc3x9710xe2x88x922, mol per dm3 of reactor volume, based on the aluminum content. However, higher concentrations are in principle also possible.
The average molecular weight of the cycloolefin copolymer formed can be controlled in a known manner by metering in of hydrogen, variation of the monomer concentrations or variation of the temperature.
The polydispersity Mw/Mn of the copolymers is very narrow, with values between 1.9 and 3.5. This results in a property profile of the polymers which makes them particularly suitable for fiber production.
As can be shown by X-ray measurements, the cycloolefin copolymers prepared by the process of the invention are partly crystalline. The degree of crystallinity of the cycloolefin copolymers is from 1 to 80%, preferably from 10 to 50%, particularly preferably from 15 to 40%.
The polymers of the invention can also be used for the preparation of polymer alloys. The alloys can be prepared in the melt or in solution. In each case the alloys confine the properties of the components in a way which is favorable for particular applications. For alloys with the polymers of the invention, the following polymers can be used:
polyethylene, polypropylene, ethylene/propylene copolymers, polybutylene, poly(4-methyl-1-pentene), polyisoprene, polyisobutylene, natural rubber, poly(methyl methacrylate), further polymethacrylates, polyacrylates, acrylate/methacrylate copolymers, polystyrene, styrene/acrylonitrile copolymers, bisphenol-A polycarbonate, further polycarbonates, aromatic polyester carbonates, polyethylene terephthalate, polybutylene terephthalate, amorphous polyarylates, nylon-6, nylon-66, further polyamides, polyaramides, polyether ketones, polyoxymethylene, polyoxyethylene, polyurethanes, polysulfones, polyether sulfones, polyvinylidene fluoride.
To obtain the cycloolefin copolymer in spinnable form, a specific workup of the reaction mixture is carried out subsequent to the polymerization step, this workup serving to reduce the residual catalyst content.
The residual catalyst content or concentration, is taken to be the concentration of compounds which are formed during the course of the polymerization, of the polymerization termination and of the workup of the reaction medium and which remain in the cycloolefin polymer. These residues are essentially compounds of the central atom of the metallocene compound and aluminum compounds. The residual catalyst contents are therefore customarily given in ppm of aluminum and ppm of metallocene metal. Since the aluminum is used in a significant excess (i.e. at least 50 fold) over the central atom, it is convenient to give the residual catalyst content in ppm of aluminum.
The residual catalyst concentration basically depends on the amount of the metallocene and of the aluminum alkyl used in the polymerization per unit amount of polymer produced. This means that the purity of both the monomers and the diluents, and also the monomer concentrations, the polymer concentrations and the catalyst activity are critical in determining the residual catalyst concentration.
Depending on the polymerization process and the catalyst content of the reaction medium, the reaction medium can be worked up in different ways. The type of workup here determines the residual catalyst concentration in the final product.
a) Termination
Only when it is possible to achieve particularly close activities in respect of the metallocene and the aluminum alkyl in the polymerization, i.e. specifically to carry out the catalysis using very small amounts of aluminum alkyl ( less than 500 ppm), can the process be carried out according to variant 1.
The polymerization termination is carried out in a vessel downstream of the polymerization reactor by addition of a terminator while stirring. The terminator is a chemical compound which reacts with the metallocene and/or the aluminum alkyl and thereby converts this/these into an unreactive form. In this variant, preference is given to selecting terminators which react with the metallocene and/or the aluminum alkyl to give compounds which are soluble in aqueous or alcoholic or ketonic solutions and are as a result separated from the cycloolefin copolymer during the precipitation process. Particular preference is given to using isopropanol, methanol, ethanol or tertbutanol as terminator.
If the terminator forms volatile compounds with the metallocene and aluminum alkyl, a reduction of the residual catalyst content can preferably be carried out together with solvent removal during a high-temperature workup such as a flash process, thin-film evaporation or a degassing extruder.
b) Precipitation
The terminated reaction medium can be fed to a precipitation. Preferred precipitants are alcohols, ketones, esters and mixtures containing these. Particular preference is given to using, as precipitants, methanol, ethanol, acetone, ethyl acetate or mixtures comprising more than 50% by volume of these compounds. Subsequently the precipitated polymer is washed at least once, for example with an aqueous, alcoholic or ketonic solution. In contrast to the description in EP 503422, solutions containing HCl or other chlorine-containing compounds may on no account be used in this washing process. Extrusion and spinning tests have shown that, at processing temperatures, cycloolefin polymers which have been washed with HCl-containing solutions are particularly prone to discolor, form pinholes or undergo localized changes which have a negative effect on the processing and the properties of these products. It is assumed that these increased changes can be attributed to the formation of various aluminum chlorides which are known to cause changes in hydrocarbons at high temperatures. Afterwards, the washed product is dried at elevated temperature, as far as possible with exclusion of oxygen, preferably under nitrogen. Drying is preferably carried out between 40xc2x0 C. below the corresponding glass transition temperature (Tg) of the polymer and 300xc2x0 C., particularly preferably between 10xc2x0 C. below Tg and 200xc2x0 C.
c) Concentration
The terminated reaction medium can, however, also be fed to a process for concentrating the reaction medium, either directly or via a further intermediate stage. The concentration is carried out in a conventional single-stage or two-stage evaporation process with the aid of flash equipment or thin-film evaporators or a combination of both. In the case of the combination, the second or last equipment item is a thin-film evaporator. The product worked up by this method is obtained as a polymer melt which can be directly granulated by conventional processes.
An intermediate stage before concentration can be, for example, a scrubbing process using an aqueous scrubbing medium. The reaction medium, which forms a two-phase mixture with the scrubbing solution, is stirred together with the scrubbing solution and subsequently decanted. It is important that the hydrophilicity of the aqueous solution is set so that no polymer goes over into the aqueous phase during scrubbing of the reaction medium. Preferred scrubbing media are alkali or chlorine-free acid aqueous or even alcohol-containing solutions. Particular preference is given to NaOH, sodium carbonate, acetic acid and sulfuric acid solutions.
This variant is preferred to variant 1, because it can also be used at higher catalyst concentrations, particularly an aluminum alkyl concentration above 500 ppm, in the reaction medium. Variant 2 comprises making the partly crystalline cycloolefin polymer in dissolved form flow at least once through a filter medium. Residual catalyst contents of less than 100 ppm of aluminum in the final polymer product are thus achieved regardless of the catalyst concentrations in the reaction medium.
A workup using such a filtration step can be carried out in different ways depending on the type of polymerization.
If, during the polymerization, the reaction medium is diluted with a solvent in which the polymer readily dissolves, preferably decalin, a hydrogenated diesel oil fraction having a boiling point between 120 and 160xc2x0 C. or cyclohexane, in a ratio of solvent to cycloolefin from 4:1 to 1:10, and/or the polymerization temperature used is relatively high, preferably from 50 to 150xc2x0 C., precipitation of the partly crystalline polymer in the form of particles can be largely avoided. Above a polymer concentration of 5%, gel formation is possible, which, if it occurs, makes it necessary, for example, to reduce the polymerization time or to further increase the polymerization temperature.
a) Termination
If the polymerization proceeds without the polymer precipitating in a heterogeneous particle form which would make possible a simple mechanical separation of the precipitated polymer from the reaction medium, the reaction medium is heated to at least 130xc2x0 C. The temperature selected is sufficiently high to ensure that the polymer is completely dissolved. So as to favor complete dissolution, an additional solvent can be added. Preference is given to hydrated diesel fractions, decalin, toluene, cyclohexane, chlorobenzene, dichlorobenzene, chloronaphthalene and naphthalene. Decalin and cyclohexane are particularly preferred. Preferred terminators in this process are those compounds which react with the metallocene and/or the aluminum alkyl used and thus give an insoluble compound. Particular preference is given to water, organic monocarboxylic, dicarboxylic and polycarboxylic acids, diols or polyols.
Subsequently a pulverulent, organic or inorganic substance which is insoluble in the reaction medium is suspended in the reaction mixture which may be diluted and in which the polymer is completely dissolved. The suspension is intimately mixed for at least 10 minutes. Preference is given to materials which are used as filter aids and also polar substances which preferably carry OH groups on their particle surface. Particular preference is given to various types of diatomaceous earth, perlites, various types of cellulose and cellulose derivatives. These insoluble substances can also be added to the reaction medium together with the terminator, so that termination and suspension are carried out simultaneously.
b) Filtration
The suspension is then filtered via a filtration layer at preferably constant temperature. The filter layer may comprise various single-layer or multi-layer filters comprising filter cloths and/or nonwoven filter fabrics and/or layers of filter aids, which in at least one layer have a porosity smaller than the average size of the particles suspended in the reaction medium. Preference is given to average porosities which are smaller than the average particle size of the suspended substance by a factor from 2 to 20, particularly by a factor from 3 to 10.
The polymer solution thus obtained can be further worked up either by precipitation or by concentration according to variant 1.
If, during the polymerization, the reaction medium is diluted with a solvent in which the polymer is sparingly soluble, preferably hexane, pentane, n-butane, iso-butane or propane in a ratio of solvent to cycloolefin from 4:1 to 0:1 and/or the polymerization temperature is between xe2x88x9270 and 150xc2x0 C., preferably between 10 and 90xc2x0 C., precipitation of the partly crystalline polymer in the form of particles can be virtually ensured. The reaction medium is thereby converted into a suspension.
This polymerization method is to be preferred to the process variant in which no polymer particles are precipitated during the polymerization. Limitation by possible gelation or deposit formation is thus avoided.
If the cycloolefin is a poor solvent for the cycloolefin polymer, so that particle formation occurs even without addition of poor solvents, polymerization in pure cycloolefin is to be preferred.
If the polymerization proceeds in such a way that the polymer precipitates in a heterogeneous particle form, a simple mechanical separation of the precipitated polymer from the reaction medium is made possible. Such a process step can of itself remove considerable amounts of metallocene and aluminum alkyl, which may be present in dissolved form, from the product to be worked up and thereby ease or simplify all further purification steps. Such a separation of the precipitated polymer particles from the rest of the reaction medium may comprise conventional filtration or be carried out with the aid of conventional centrifugation processes. The polymer-free reaction medium can be recirculated into the polymerization. To ensure that such recycling does not impair catalysis, the removal of the polymer from the filter or from the centrifuge must be carried out under inert conditions. The advantage of this separation is, inter alia, that in the subsequent dissolution process the residual monomers no longer have to be heated to higher temperatures at which secondary reactions, cracking and fish eye formation can occur, all of which have a negative effect both on the overall monomer yield and also on the uniformity and purity of the final polymer product.
The removed polymer is then dissolved in a solvent at elevated temperature. Solution temperatures from 130 to 200xc2x0 C. are preferred. The selected temperature is sufficiently high to ensure that the polymer is completely dissolved. Preferred solvents are hydrogenated diesel fractions, decalin, toluene, cyclohexane, chlorobenzene, dichlorobenzene, chloronaphthalene and naphthalene. Particular preference is given to decalin, chlorobenzene, dichlorobenzene and cyclohexane. This solution can, using the procedure described under variant 2.1., be admixed with terminator and insoluble substances, filtered hot and subsequently be further worked up by means of the precipitation described under variant 1 or by concentration.
The workup process of the invention can also, in addition to the catalyst systems described here (metallocenes and aluminum alkyls), be applied to the removal of other catalyst systems (for example Ziegler catalysts) which can be used for cycloolefin polymerization.
The cycloolefin copolymers worked up according to the invention are particularly suitable for the production of fibers. The fibers can be spun from the melt using conventional industrial processes. The spinning solution and also the polymer melt can additionally be freed of particles and gel particles by a further filtration.
If the melting point of the cycloolefin copolymer lies above 300xc2x0 C., the polymer can be made into a paste using high-boiling hydrocarbons so as to improve the processability. In a melt-spinning process, the polymer is melted in a single-screw or twin-screw extruder or in a piston extruder. Melting in a piston extruder can be carried out by heating the barrel. A further possibility is to press the polymer against a heated grid, whereupon the polymer melts. The polymer melt then flows through a spinning head having one or more spinnerets. The fiber or filaments are preferably wound onto bobbins at an increased take-off rate.
The melt-spun fiber is preferably further drawn while being heated. Here the fiber is passed through one or more heating zones, with it being possible to set different drawing conditions. Preferably, high draw ratios are used, by which means the crystallinity of the fiber is further increased.
The fiber or filaments are generally drawn so as to achieve high mechanical strength and high elastic moduli. The draw ratio is usually from 1.1 to 50, preferably from 1.5 to 30, particularly preferably from 2 to 10.
Drawing can be carried out in a single step, or in two or even more steps. Furthermore, the fibers or filaments can be subjected to heat treatment at the same or a higher temperature so as to increase the crystallinity. Heat transmission can be effected by means of a hot plate (which may be curved) or cylindrical devices.
The drawing temperatures advantageously lie between the glass transition temperature and the melting point. For cycloolefin copolymers of the invention, the first drawing is carried out at temperatures between 100 and 500xc2x0 C., preferably between 120 and 300xc2x0 C.
A subsequent thermal after treatment at the same or a higher temperature than the drawing temperature with application of a small tensile stress serves to set the fiber. A tendency to shrink at higher temperatures is thereby reduced.
The spinning speed can be up to 5000 m/min or more. Highly oriented as-spun yarns can thus be obtained, these requiring only a small amount of additional drawing. The drawing of the fibers is in accordance with the desired elongation at break, the drawing generally being carried out in such a way as to obtain elongations at break of 2-50%, preferably 10-40%, particularly preferably 15-30%.
The drawn fibers have tensile strengths from 70 to 1000 MPa, preferably from 200 to 800 MPa, particularly preferably from 300 to 500 MPa. The linear density of the fiber lies in the range from 0.01 to 100 g/km, preferably from 0.05 to 20 g/km, particularly preferably from 0.2 to 10 g/km. The modulus lies in the range from 2 to 20 GPa, preferably from 5 to 10 GPa, particularly preferably from 6 to 8 GPa.
The fiber of the invention can, for example, be used as an industrial fiber, in woven fabrics for the textile sector and in industry or in nonwovens. Filaments, multifilaments, ropes and cables can be produced. The excellent hydrolysis resistance and UV resistance deserve emphasis. Likewise, the good strength at elevated temperature deserves mention.
The glass transition temperatures Tg given in the following examples were determined by DSC (Differential Scanning Calorimetry) at a heating rate of 20xc2x0 C./min. The viscosity numbers given were determined in accordance with DIN 53 728.
The residual catalyst content was determined as aluminum content by X-ray fluorescence spectroscopy.
The norbornene content in the cycloolefin copolymer was determined by quantitative 13C-NMR spectroscopy.